1. Field of the Invention
The present invention relates to an improved injection molding apparatus and method in which a three-way shut off valve can be controlled to allow molten material (i) to pass through the valve, (ii) to be blocked by the valve, or (iii) to be diverted to a purging channel. Preferably, the three-way shut off valve is used in conjunction with an articulated coupling which allows molten material to be transmitted between an injection unit and a hot runner system in a movable mold component. The valve may also be used with an injection nozzle to allow molten material to be transmitted between an injection unit and either a standard cold runner mold or a standard hot runner mold.
2. Description of Related Art
In some injection molding applications, shut-off valves are used to control the flow of the molten material from the injection unit to the hot runner system. Typically, the injection unit actually disengages from the mold in order to purge the molten material from a portion of the melt channel. Thus, the remaining molten material is exposed to contact with air after purging. This may cause surface defects on molded parts depending on material grade and surface quality requirements.
U.S. Pat. No. 4,140,238 to Dawson discloses a pneumatically driven plunger type shut off valve in an injection molding nozzle. The plunger has two positions—open and blocked. There is no disclosure, however, of a third position for the plunger.
Japanese Publication 56-93528 to Kouhei Koga discloses a piston driven plunger type shut off valve that acts as the injection channel conduit to the mold. The plunger contains the melt channel and connects to the shooting pot cylinder in the plunger's forward position. In the plunger's retracted position the melt passes around the plunger's exterior surface via a channel created by locally reducing the external diameter of the plunger. There is no disclosure of a third position for the plunger.
U.S. Pat. No. 4,966,545 to Brown discloses a hot runner shooting pot plunger that uses a first piston to actuate a first portion of its stroke, and a second piston coaxially aligned with the first piston to actuate a second portion of its stroke. The plunger is thereby controlled to move to each of three positions by the two pistons. The plunger does not act as a shut-off valve.
PCT publication WO 00/74920 to Catoen discloses a hot runner valve gate having a single valve stem movable to three distinct positions by two nested pneumatic pistons coaxially mounted at one end of the valve stem. In the first position the nozzle opens to permit flow of the material, in the second (intermediate) position the nozzle blocks the flow of the material, and in the third position the stem is extended through the gate orifice and projected forward to clear any blockage in the downstream melt channel. In the third position the melt channel is blocked by the stem and material cannot flow. There is no disclosure of using the valve to direct the material into a second channel when the third position is selected.
Thus, what is needed is an injection molding three way valve which can effectively and efficiently control the flow of melt so that it is provided to the hot runner, or shut off, or provided to a purging channel, all with minimal structure and time and within the operating environment of the injection molding machine.